With people's increasing demands for wireless communications, and the rapid development of wireless multimedia services, in order to realize convergence of mobile communications and wideband wireless access, provide a higher data rate, and improve system performance, two main technologies, multiple-input multiple-output (Multiple-Input Multiple-Output, MIMO) and orthogonal frequency division multiplexing (Orthogonal Frequency Division Multiplexing, OFDM), are adopted in both the fourth generation mobile communication system (4G) and the long term evolution (Long Term Evolution, LTE) standards. Generally, the MIMO technology in which multiple antennas are used to perform wireless transmission may greatly increase system capacity and spectral efficiency without the need to add time frequency resources, and has a high value of application. The OFDM technology has advantages such as high spectrum utilization and anti-multipath fading, and is commonly regarded as a core technology for the 4G and LTE standards.
In the MIMO technology, multiple antennas are used to suppress channel fading and a data rate may be increased. With the increase of the number of antennas, a MIMO system not only multiplies in channel capacity, but also can provide a spatial diversity gain.
The OFDM is one type of multi-carrier modulation (MCM, Multi-Carrier Modulation) and its main idea is: dividing a channel into several orthogonal subchannels, converting a high-speed data signal into a parallel low-speed sub-data stream, which are modulated onto each subchannel for transmission. Orthogonal signals may be separated by adopting a related technology at a receiving end, so that mutual interference ICI among the subchannels may be reduced. A signal bandwidth on each subchannel is smaller than a related bandwidth of the channel, so that it may be regarded as flat fading on each subchannel, thereby eliminating inter-symbol interference. Moreover, because a bandwidth of each subchannel is only a small part of a bandwidth of an original channel, channel equalization becomes relatively easy. In the process of evolution to 3G/4G, the OFDM is one of the key technologies, which may combine technologies of diversity, space-time coding, interference and inter-channel interference suppression, and smart antenna, and improve the system performance to a maximum degree. The following types are included: V-OFDM, W-OFDM, F-OFDM, MIMO-OFDM, and multiband-OFDM.
In a wireless channel condition where time-varying multipath fading and interference noise coexist, an OFDM multi-carrier transmission technology has a strong anti-fading capability, is insensitive to narrowband interference and narrowband noise, has high spectral efficiency, and supports a variable user rate, and all these characteristics make it a mainstream access solution in the 4G mobile communication system and LTE standards. However, an OFDM system has the problem of a high peak-to-average ratio. To overcome an excessively high peak-to-average ratio of the OFDM and in consideration of the cost of a mobile terminal, a single carrier sending technology, namely, a technology based on the discrete fourier transform spread orthogonal frequency division multiplexing (DFT-Spread OFDM, DFT-S-OFDM), is formally adopted as a baseband modulation technology for an LTE uplink. In the DFT-S-OFDM technology, frequency domain spread processing of data is added on the basis of conventional OFDM transmission, so that peak-to-average ratio performance that is close to single carrier transmission is obtained, implementation is convenient, and flexible subcarrier allocation can be performed for different users, thereby meeting uplink requirements.
A receiver is an important component of a wireless communication system, a receiver with good performance is critical to the entire system, and a detection algorithm is the core of the receiver. However, due to characteristic of a technical system of a single carrier system, in its MIMO receiver, an algorithm that is similar to an MLD (maximum likelihood detection) algorithm commonly adopted in a MIMO-OFDM system cannot be adopted, while another MMSE-based parallel interference detection method that may be considered for use has disadvantages such as a long delay and low iterative interference cancellation efficiency, resulting in high implementation complexity and unsatisfying detection performance.
In an existing space division multiplexing MIMO-OFDM system, a commonly-used type of transceiver is V-BLAST, and a typical type of method for its MIMO detection is to perform QRD on a channel matrix to achieve the objective of partial stream separation. Next, a layer-by-layer IC method is adopted to cancel interference caused by another stream, and then sending stream detection is performed layer by layer through simple equalization processing. For the OFDM system, symbol modulation is in a frequency domain, therefore, serial interference cancellation equalization detection may be performed subcarrier by subcarrier. However, for the single carrier system, due to different signal sending models and characteristics that equalization processing is in the frequency domain while detection of a modulation symbol needs to be in a time domain, currently there is no detection method with high performance and low complexity.